The invention relates to safety equipment for a tank having a system for collecting the gas expelled from the tank during loading.
When a certain volumetric quantity of product per time unit, e.g. measured in m.sup.3 /h, is loaded into a tank, a volumetric quantity of gas is to be expelled from the tank per time unit corresponding to the volumetric quantity of product loaded per time unit with an addition, where applicable, for evaporation or other gas evolution from the liquid surface in the tank.
The traditional expedient for controlling this discharge of gas is a pressure relief valve mounted on the tank, through which the gas is blown off into the surrounding atmosphere.
However, attention is being paid to a still increasing extent to the fact that the gases blown off into the surrounding atmosphere may give rise to environmental pollution or may even be directly poisonous and harmful to the crew and other persons present in the area. At many loading stations it is therefore today a requirement that the gas expelled during loading should not be blown off into the surrounding atmosphere, but should be collected for returning to the loading station, where it may be fed back into the storage tank from which loading takes place, or may be conducted to a system for destruction, e.g. by incineration, or for liquefaction, regeneration or other processing, or in some cases to an atmospheric outlet fulfilling strict requirements of the authorities in respect of location and blow-off characteristics.
To be accepted for loading at a loading station having such gas disposal facilities, a tanker must have a gas collecting system having an outlet for connection to a gas receiving inlet of the loading station, e.g. by means of a hose. Said outlet and inlet must both be provided with a stop valve, which is to be opened before loading is commenced and to be closed when loading has been completed.
If however, by human error or negligence, it is forgotten to open either one or both of the stop valves before commencing loading, there is a danger that loading may be continued after the tank pressure has risen above the maximum permissible value for which the tank is designed. This may result in explosion of the tank.